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Abstract

The Arkoma Basin is a Carboniferous peripheral foreland basin creating a structural depression covering an approximate area of 33,800 miles2 that extends through east-central Oklahoma and west-central Arkansas. The entire basin fill includes Pre-Mississippian carbonate shelf deposits, Mississippian marine carbonates and black shales, and Pennsylvanian mixed carbonated/clastic and shore zone/deltaic deposits. The Lower Atoka formation (Pennsylvanian) occurs in outcrop along the southern Boston Mountain Plateau in northern Arkansas and extends into the subsurface of the Arkoma Basin over an area of 2,300 miles2. The Lower Atoka ranges from 600 to 1500 feet in thickness and represents a cyclic succession of stacked shelf to shore zone/deltaic deposits recording a single 3rd order (1-10 m.y.) Vail/Exxon depositional sequence. It was deposited across a broad, tectonically stable platform along the southern margin of Laurasia just before its collision with the Gondwana and the formation of Pangea at the end of the Paleozoic. Tectonic influences meant that it was not a 100% stable platform during the Lower Atoka deposition. This affected the deposition of all the sequences in the Lower Atoka. Topographic relief on preceding deposition also helped create areas of accommodation space filled by offset, compensation bedding. Finally, subsidence on a passive margin has been argued to be up to almost 4 km. This helps explain the “long distance” shoreline shifts and cyclicity in the current time of deposition. This means that these 4th to 5th order cycles (10’s to 100’s k.y.) may reflect glacio eustacy and sediment supply and can be correlated across the entire area or a very large area. In addition, there appears to be a tectonic over print that influences onlap edges that define northern limits and areas of bypass and nondeposition.

Lateral variation in facies and sand content as well as proximal to distal changes in depositional architecture have been defined by high resolution correlation and log motif analysis of several hundred wells along the northern margin of the basin. This work provides an excellent case history for the definition of stratigraphic architecture and internal reservoir body geometries within individual cycles in a single 3rd order depositional sequence.